Question

A privacy engineer is designing a healthcare records system where patient national ID numbers must be stored confidentially but must also support exact-match lookups by authorized staff. The team proposes standard randomized AES-256 encryption for the field. During testing, they discover that lookups require decrypting every row to find a match, which is unacceptable at scale. Which technique BEST preserves confidentiality while enabling efficient exact-match search on the encrypted values?

Accepted Answer

Deterministic encryption of the national ID field, with strict key access controls

Answer

Store the plaintext national ID in an indexed column and rely on database access controls

Answer

Apply format-preserving encryption and remove the index to reduce exposure

Answer

Hash the national ID with an unsalted SHA-256 digest and index the hash